1. Field of the Invention
The present invention relates to a damper unit for a vessel propulsion apparatus, a propeller for a vessel propulsion apparatus including the damper unit, and a vessel propulsion apparatus including the damper unit.
2. Description of the Related Art
A propeller for a vessel propulsion apparatus is mounted on a propeller shaft via a propeller damper (damper unit). The damper unit transmits a torque between the propeller and the propeller shaft and absorbs a vibration between the propeller and the propeller shaft. An impact (shift shock) accompanying engagement/disengagement of a dog clutch and an impact accompanying collision of the propeller and an underwater obstacle are absorbed by the damper unit. The damper unit thus contributes to the protection of parts, reduction of impact noise, and improvement of maneuverability.
A damper unit according to U.S. Patent Application Publication No. 2011/0212657 A1 includes two dampers (a main damper and a sub damper) disposed in parallel. In a case in which a torque applied to the propeller or the propeller shaft is small, only the main damper, which is softer than the sub damper, transmits the torque. When the torque applied to the propeller or the propeller shaft increases, the torque is transmitted by two parallel paths (a path via the main damper and a path via the sub damper). That is, when the torque applied to the propeller or the propeller shaft increases, both dampers transmit the torque.